Health officials are urging Americans to not let their guards down against COVID-19 as researchers discover new variants that may already be more transmissible and could also be somewhat resistant to the vaccine.

“At this level of cases, with variants spreading, we stand to completely lose the hard-earned ground we have gained,” Centers for Disease Control and Prevention director Dr. Rochelle Walensky said during a White House briefing Monday. “These variants are a very real threat to our people and our progress.”

While experts have been following variants first identified in the United Kingdom and South Africa, they're also seeing red flags in other variants discovered closer to home in Brazil, New York and California. 

In Monday’s briefing, Dr. Anthony Fauci said a recent study found some COVID-19 treatments may not be as effective against the new variant discovered in New York.